Cisco Routers running Internetwork Operating System (IOS) that supports Multi Protocol Label Switching (MPLS) are vulnerable to a Denial of Service (DoS) attack on interfaces where MPLS is not configured. A system that supports MPLS is vulnerable even if that system is not configured for MPLS. The vulnerability is only present in Cisco IOS release trains based on 12.1T, 12.2, 12.2T, 12.3 and 12.3T. Releases based on 12.1 mainline, 12.1E and all releases prior to 12.1 are not vulnerable. Cisco has made free software available to address this vulnerability. There are workarounds available to mitigate the effects. This issue is tracked by CERT/CC VU#583638. This advisory is available at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20050126-les.
Cisco Routers running Internetwork Operating System (IOS) that supports Multi Protocol Label Switching (MPLS) are vulnerable to a Denial of Service (DoS) attack on interfaces where MPLS is not configured. A system that supports MPLS is vulnerable even if that system is not configured for MPLS.
The vulnerability is only present in Cisco IOS release trains based on 12.1T, 12.2, 12.2T, 12.3 and 12.3T. Releases based on 12.1 mainline, 12.1E and all releases prior to 12.1 are not vulnerable.
Cisco has made free software available to address this vulnerability.
There are workarounds available to mitigate the effects.
This issue is tracked by CERT/CC VU#583638.
This advisory is available at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20050126-les.
This section provides details on affected products.
Only the following products running a vulnerable version of IOS that support MPLS are affected.
Products that are not listed above are not affected.
MPLS is not supported in IP and IP Plus feature sets. Therefore, products running an IOS version with an IP or IP Plus feature set are not vulnerable.
An attack can only be launched at systems that are not configured for MPLS Traffic Engineering and on the interfaces where MPLS is not enabled. MPLS enabled interfaces can be determined by the show mpls interfaces command.
An unaffacted system where MPLS is not supported will give an output similar to the following.
Router#show mpls interfaces ^ % Invalid input detected at '^' marker. Router#
MPLS can be enabled in different ways on a router. In the below output, a router is shown that has MPLS enabled for IP on interface Ethernet0/0.
Router#show mpls interfaces Interface IP Tunnel Operational Ethernet0/0 Yes (tdp) No Yes Router#
When MPLS for IP is enabled on an interface, the router is immune to the attacks coming from that interface but vulnerable to the attacks coming from other interfaces. Enabling MPLS for IP on all interfaces of the router will make the router immune to attacks coming from any interface. An interface that has MPLS for IP enabled will have mpls ip or tag-switching ip command in the interface configuration.
MPLS Traffic Engineering (TE) provides a better protection against this vulnerability. If MPLS TE is enabled globally, the router will be immune to the attacks coming from any interface. A router that has MPLS TE enabled will have mpls traffic-eng tunnels command in the show running-config output.
These products are not vulnerable:
No other Cisco products are currently known to be affected by these vulnerabilities.
Multi Protocol Label Switching (MPLS) is a vendor-independent protocol that integrates layer-2 (as defined in the Open System Interconnection Reference Model) information into layer-3. More information on MPLS can be found at http://www.cisco.com/warp/public/732/Tech/mpls.
A vulnerability exists in the processing of an MPLS packet that is received on an interface where MPLS is disabled. A router that is configured for MPLS Traffic Engineering is immune to attacks coming from any interface.
A Cisco device receiving a crafted packet on an MPLS disabled interface will reset and may take several minutes to become fully functional. This vulnerability may be exploited repeatedly resulting in an extended DoS attack. This issue is documented in bugs ID CSCeb56909 ( registered customers only) and CSCec86420 ( registered customers only) .
Such crafted packets can only be sent from the local network segment.
The effectiveness of any workaround is dependent on specific customer situations such as product mix, network topology, traffic behavior, and organizational mission. Due to the variety of affected products and releases, customers should consult with their service provider or support organization to ensure any applied workaround is the most appropriate for use in the intended network before it is deployed.
Warning: Using this workaround may affect the operation of your network and might cause problems. Therefore it is strongly recommended that you do a code upgrade if you are affected. It is not recommended that you use the workaround as a long term solution.
Enabling MPLS Traffic Engineering (MPLS TE) globally can be used as a workaround to mitigate this vulnerability. Since MPLS requires Cisco Express Forwarding (CEF) in order to work, CEF needs to be enabled first in order to enable MPLS TE.
CEF and MPLS TE can be enabled by the following commands.
Router(config)# ip cef Router(config)# mpls traffic-eng tunnels
Having MPLS TE enabled will make the router immune to the attacks coming from any interface.
When considering software upgrades, also consult http://www.cisco.com/go/psirt and any subsequent advisories to determine exposure and a complete upgrade solution.
In all cases, customers should exercise caution to be certain the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, contact the Cisco Technical Assistance Center ("TAC") or your contracted maintenance provider for assistance.
Each row of the Cisco IOS software table (below) describes a release train and the platforms or products for which it is intended. If a given release train is vulnerable, then the earliest possible releases that contain the fix (the "First Fixed Release") and the anticipated date of availability for each are listed in the "Rebuild" and "Maintenance" columns. A device running a release in the given train that is earlier than the release in a specific column (less than the First Fixed Release) is known to be vulnerable. The release should be upgraded at least to the indicated release or a later version (greater than or equal to the First Fixed Release label).
For more information on the terms "Rebuild" and "Maintenance," consult the following URL:
http://www.cisco.com/warp/public/620/1.html
Major Release |
Availability of Repaired Releases |
||
---|---|---|---|
Affected 12.1-Based Release |
Rebuild |
Maintenance |
|
12.1DB |
Migrate to 12.3(4)T or later |
||
12.1DC |
Migrate to 12.3(4)T or later |
||
12.1T |
Migrate to 12.2 or later |
||
12.1XG |
Migrate to 12.3 or later |
||
12.1XI |
Migrate to 12.2 or later |
||
12.1XJ |
Migrate to 12.3 or later |
||
12.1XL |
Migrate to 12.3 or later |
||
12.1XM |
Migrate to 12.3 or later |
||
12.1XP |
Migrate to 12.3 or later |
||
12.1XQ |
Migrate to 12.3 or later |
||
12.1XR |
Migrate to 12.3 or later |
||
12.1XT |
Migrate to 12.3 or later |
||
12.1XU |
Migrate to 12.3 or later |
||
12.1XV |
Migrate to 12.3 or later |
||
12.1YA |
Migrate to 12.3 or later |
||
12.1YB |
Migrate to 12.3 or later |
||
12.1YC |
Migrate to 12.3 or later |
||
12.1YD |
Migrate to 12.3 or later |
||
12.1YE |
Migrate to 12.3 or later |
||
12.1YF |
Migrate to 12.3 or later |
||
12.1YH |
Migrate to 12.3 or later |
||
12.1YI |
Migrate to 12.3 or later |
||
Affected 12.2-Based Release |
Rebuild |
Maintenance |
|
12.2 |
12.2(10g) |
||
12.2(13e) |
|||
12.2(16f) |
|||
12.2(17d) |
|||
12.2(19b) |
|||
12.2(21a) |
|||
12.2(23) |
|||
12.2B |
12.2(2)B through 12.2(4)B7, Migrate to 12.3 or later |
||
12.2(4)B8 and forward, Migrate to 12.3(4)T or later |
|||
12.2BC |
12.2(15)BC2 |
||
12.2BW |
Migrate to 12.3 or later |
||
12.2BX |
Migrate to 12.3(7)XI1 or later |
||
12.BY |
Migrate to 12.3(4)T or later |
||
12.2BZ |
Migrate to 12.3(7)XI1 or later |
||
12.2CX |
Migrate to 12.2(15)BC2 |
||
12.2CY |
Migrate to 12.2(15)BC2 |
||
12.2CZ |
12.2(15)CZ |
||
12.2DA |
12.2(12)DA6 |
||
12.2DD |
Migrate to 12.3(4)T or later |
||
12.2DX |
Migrate to 12.3(4)T or later |
||
12.2EW |
12.2(18)EW |
||
12.2EWA |
12.2(20)EWA |
||
12.2JA |
12.2(15)JA |
||
12.2JK |
12.2(15)JK |
||
12.2MB |
Migrate to 12.2(19)SW |
||
12.2MC |
Migrate to 12.3(11)T |
||
12.2MX |
Migrate to 12.3(8)T or later |
||
12.2SU |
12.2(14)SU |
||
12.2SW |
12.2(19)SW |
||
12.2SY |
Migrate to 12.2(17d)SXB or later |
||
12.2SZ |
Migrate to 12.2(20)S4 |
||
12.2T |
12.2(13)T14 |
||
12.2(15)T7 |
|||
12.2XA |
Migrate to 12.3 or later |
||
12.2XB |
12.2(2)XB18 |
||
12.2XC |
Migrate to 12.3T or later |
||
12.2XD |
Migrate to 12.3 or later |
||
12.2XE |
Migrate to 12.3 or later |
||
12.2XF |
Migrate to 12.2(15)BC2 |
||
12.2XG |
Migrate to 12.3 or later |
||
12.2XH |
Migrate to 12.3 or later |
||
12.2XI |
Migrate to 12.3 or later |
||
12.2XJ |
Migrate to 12.3 or later |
||
12.2XK |
Migrate to 12.3 or later |
||
12.2XL |
Migrate to 12.3 or later |
||
12.2XM |
Migrate to 12.3 or later |
||
12.2XN |
Migrate to 12.3 or later |
||
12.2XQ |
Migrate to 12.3 or later |
||
12.2XR |
12.2(15)XR |
||
12.2XS |
Migrate to 12.3 or later |
||
12.2XT |
Migrate to 12.3 or later |
||
12.2XU |
Migrate to 12.3 or later |
||
12.2XV |
No plan. |
||
12.2XW |
Migrate to 12.3 or later |
||
12.2XZ |
Migrate to 12.3 or later |
||
12.2YA |
12.2(4)YA8 |
||
12.2YB |
Migrate to 12.3 or later |
||
12.2YC |
Migrate to 12.3 or later |
||
12.2YD |
Migrate to 12.3(8)T or later |
||
12.2YE |
Migrate to 12.2(18)S or later |
||
12.2YF |
Migrate to 12.3 or later |
||
12.2YG |
Migrate to 12.3 or later |
||
12.2YH |
Migrate to 12.3 or later |
||
12.2YJ |
Migrate to 12.3 or later |
||
12.2YL |
Migrate to 12.3T or later |
||
12.2YM |
Migrate to 12.3T or later |
||
12.2YN |
Migrate to 12.3T or later |
||
12.2YO |
Migrate to 12.2(17d)SXB or later |
||
12.2YQ |
Migrate to 12.3(4)T or later |
||
12.2YR |
Migrate to 12.3(4)T or later |
||
12.2YS |
Migrate to 12.3T or later |
||
12.2YU |
Migrate to 12.3(2)T or later |
||
12.2YV |
Migrate to 12.3(4)T or later |
||
12.2YW |
Migrate to 12.3(2)T or later |
||
12.2YX |
Migrate to 12.2(14)SU |
||
12.2YZ |
Migrate to 12.2(20)S4 |
||
12.2ZB |
Migrate to 12.3T or later |
||
12.2ZC |
Migrate to 12.3T or later |
||
12.2ZD |
Migrate to 12.3 or later |
||
12.2ZE |
Migrate to 12.3 or later |
||
12.2ZF |
Migrate to 12.3(4)T or later |
||
12.2ZG |
Migrate to 12.3(4)T or later |
||
12.2ZH |
Migrate to 12.3(4)T or later |
||
12.2ZI |
Migrate to 12.2(18)S or later |
||
12.2ZJ |
Migrate to 12.3T or later |
||
12.2ZL |
Migrate to 12.3(7)T or later |
||
12.2ZN |
Migrate to 12.3T or later |
||
12.2ZO |
Migrate to 12.3 or later |
||
12.2ZP |
No plan. |
||
Affected 12.3-Based Release |
Rebuild |
Maintenance |
|
12.3 |
12.3(3f) |
||
12.3(5) |
|||
12.3B |
12.3(5a)B4 |
||
12.3BC |
12.3(9a)BC |
||
12.3BW |
Migrate to 12.3(5a)B or later |
||
12.3T |
12.3(2)T5 |
||
12.3(4)T7 |
|||
12.3(7)T |
|||
12.3XA |
Migrate to 12.3(7)T or later |
||
12.3XB |
Migrate to 12.3(8)T or later |
||
12.3XC |
Migrate to 12.3(2)XC3 - Availablility date TBD |
||
12.3XD |
12.3(4)XD |
||
12.3XE |
12.3(2)XE1 |
||
12.3XF |
12.3(2)XF |
||
12.3XG |
12.3(4)XG1 |
||
12.3XH |
12.3(4)XH |
||
12.3XI |
12.3(7)XI |
||
12.3XJ |
12.3(7)XJ |
||
12.3XK |
12.3(4)XK1 |
||
12.3XL |
12.3(7)XL |
||
12.3XM |
12.3(7)XM |
||
12.3XN |
12.3(4)XN |
||
12.3XQ |
12.3(4)XQ |
||
12.3XR |
12.3(7)XR |
||
12.3XS |
12.3(7)XS |
||
12.3XT |
12.3(2)XT |
||
12.3XU |
12.3(8)XU |
||
12.3XW |
12.3(8)XW |
||
12.3XX |
12.3(8)XX |
||
12.3XY |
12.3(8)XY |
||
12.3YA |
12.3(8)YA |
||
12.3YD |
12.3(8)YD |
||
12.3YE |
12.3(4)YE |
||
12.3YF |
12.3(11)YF |
||
12.3YG |
12.3(8)YG |
||
12.3YH |
12.3(8)YH |
When considering software upgrades, please also consult http://www.cisco.com/en/US/products/products_security_advisories_listing.html and any subsequent advisories to determine exposure and a complete upgrade solution.
In all cases, customers should exercise caution to be certain the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, contact the Cisco Technical Assistance Center (TAC) for assistance.
The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability described in this advisory.
To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
Revision 1.1 |
2005-January-28 |
Clarified wording in Summary section. Added version 12.2(15)T7 to Software Versions and Fixes table. Removed versions 12.2S, 12.2SX, 12.2SXA, 12.2SXB and 12.2SXD from the Software Versions and Fixes table. |
Revision 1.0 |
2005-January-26 |
Initial public release. |
THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.
A stand-alone copy or paraphrase of the text of this document that omits the distribution URL is an uncontrolled copy, and may lack important information or contain factual errors. The information in this document is intended for end-users of Cisco products.